Argon is a highly inert element used in the some high-temperature industrial processes, such as steel-making where ordinarily non-reactive substances become reactive. Argon is also used in various types of metal fabrication processes such as arc welding as well as in the electronics industry, for example in silicon crystals growing processes. Still other uses of argon include medical, scientific, preservation and lighting applications.
Argon constitutes a minor portion of ambient air (i.e. 0.93%), yet it possesses a relatively high value compared to the oxygen and nitrogen products recovered from air separation units. Argon is typically recovered from the Linde-type double column arrangement by extracting an argon rich draw from the upper column and directing the stream to a third column or crude argon column to recover the argon. Crude argon produced in this “superstaged” distillation process typically includes an argon condensing unit disposed within the argon column or situated between the argon column and the upper column of the Linde-type double column arrangement to produce the argon product. The argon condensation load is typically imparted to a portion of the oxygen rich column bottoms (e.g. kettle) prior to its introduction into the lower pressure distillation column.
Drawbacks of the typical three column argon producing air separation unit are the additional capital costs associated with argon recovery and the resulting column/coldbox heights, often in excess of 200 feet, are required to recover the high purity argon product. As a consequence, considerable capital expense is incurred to attain the high purity argon, including capital expense for split columns, multiple coldbox sections, argon condensing assembly, liquid reflux/return pumps, etc.
One particular concern is the argon condensing assembly used in many conventional air separation plants. The conventional argon condensing assembly consists of a large separation vessel containing multiple thermo-syphon type condensers and due to its size and external plumbing requirements and often increases the height of the air separation cold box. Some prior art solutions have addressed the column/coldbox heights by placing the argon condensing assembly in a separate vessel that is hung between the argon column and the low pressure column in lieu of stacking the argon condensing assembly above the argon column. In either arrangement, the argon vapor is typically drawn into the top of each condensing assembly via a manifold and is completely condensed with a portion of the kettle liquid from the higher pressure column or with cold vapor from the lower pressure column. In many prior art argon condensing assemblies, the condenser is disposed in a large separation vessel and partially submerged in a bath of the kettle liquid. The kettle liquid is typically drawn into the bottom of the condensers and flows upwards, boiling as it absorbs heat from the argon vapor. From a safety perspective, it is crucial to prevent complete vaporization of the kettle liquid within the boiling passages to ensure that there is adequate liquid to keep the surfaces are wetted. This is particularly important where the kettle liquid input to each condense is a two phase flow.
There is a continuing need to develop an improved argon recovery process or arrangement which can enhance the safety, performance and cost-effectiveness of argon recovery in cryogenic air separation units, and in particular, to develop a more compact lower cost argon condensing assembly.